Up to 30 per cent of parents believe their children have food allergies when in fact only between 4 and 8 per cent of children do, a report in the Canadian Medical Association Journal says.

Among adults, as many as 30 per cent believe they suffer from food allergies, when the actual incidence is 1 or 2 per cent, says McGill University pediatric allergist Rhoda Kagan, one of the authors of a paper in today's edition of the journal.

It is common for parents to assume that a rash or intestinal tract problem that appears after their child ate a particular food was caused by an allergic reaction, Dr. Kagan said in an interview.

She said parents who suspect their child has an allergy should visit an allergist to have it confirmed with skin tests or blood work before they eliminate healthy foods from their child's diet.

She noted that it takes a lot of vigilance to protect a child with food allergies. A family's eating habits have to change, and friends and school officials have to be warned.

"If they aren't allergic, then you don't have to go through that."

Her report notes that eight foods are responsible for 90 per cent of food allergies: cow's milk, eggs, soy, wheat, peanuts, nuts that grow on trees (walnuts, hazelnuts, almonds, cashews, pecans and pistachios) and fish and shellfish.

With adults, she says, many people confuse a food intolerance with the more severe problem of an allergy.

Being lactose-intolerant means that drinking cow's milk makes you feel uncomfortable. It doesn't mean that a sip of milk might cause your airway to swell so much you couldn't breathe.

All food allergies have the potential to induce anaphylaxis, a potentially fatal allergic reaction. It happens when the body overproduces an antibody known as IgE in response to an exposure.

The IgE antibodies latch on to mast cells, which, among other things, line the nose, lungs and skin. The cells then pump out histamine and other chemicals that produce the allergic reaction -- from hives to constricted air flow.

Allergies to peanuts and other nuts account for most emergency-room visits caused by anaphylactic reactions.

Dr. Kagan recently published research that found peanut allergies may be on the rise in Quebec. The two-year survey of 8,000 elementary students found that 1.5 per cent of children in the province have an allergy to peanuts.

That was higher than previous North American and European estimates that 0.5 per cent of children are allergic.

Peanut allergies are particularly troubling because they develop very early in life, often before the age of 2.

Highly sensitive individuals can react to even trace amounts of peanuts.

Dr. Kagan said increased public awareness about peanut allergies may partly account for why so many parents worry their children have food allergies.

There is also strong evidence that childhood asthma and seasonal allergies are increasing, she said, adding that this may also be heightening fears of food allergies.